Run time and re-charging rates will be equivalent. As warped says, the voltage will be less so the car will be slower. Not recommended for Stock classes, just 'motor up' if you're running Modified.
Yes, as it stands, LiFe and LiPo have an equivalent life.
6.6v is enough to power all your electrics. They all require 6v minimum, and even under load you should be over that. 6.6v is the fully discharged voltage, which is still well above the 6v fully discharged NiMh we used to use!
Unless you use a cut-off the battery will go to zero and be damaged, just like LiPo. However, you can't use a LiPo cut-off as that will be 7.4v. If you use a Tekin speedo you can select a custom cut-off voltage, but all other speedos I know of, and specialist cut-off devices, will be at too high a voltage. Don't run the cells flat, you'll wreck them - use a cut-off.
For now, I would suggest that LiFe is good for Club if you can motor-up, but not for competition. They are great as receiver packs though! HTH
